The Fresh Water Flush (FWF) extends the life of the membranes by rinsing them with fresh water by merely a touch of a button. When the FWF is activated, it will remove all salt water from the internal parts of the system and flush the membranes with clean fresh water preventing saltwater corrosion of the internal parts and reducing biological fouling of the RO membrane. The Fresh Water Flush automatically repeats itself every seven days!